Gas replacement of metal sulfides



DeC- 8, 1953 E. s. ROBERTS ETA. 2,662,009

I GAS REPLACEMENT OF'METAL SULFIDES Filed NOV. 15, 1949 4 Sheets-SheetI l i i I l I l i lDec- 8, 1953 E.v s. ROBERTS Erm. 2,662,009

GAS REPLACEMENT OF METAL SULFIDES Filed Nov. 15, 1949 4 Sheets-Sheet 2 ATTORNEY Dec. 8, 1953 E. S. ROBERTS ETAL GAS REPLACEMENT OF METAL SULFIDES Filed Nov. 15, 1949 4 Sheets-Sheet 3 INVENTORS 50mg/P0 5, ,Paez-f? 75,

' ATTONY' Reduc/'ily G05 D 8, 1953 E. s. ROBERTS Erm. 2,652,009

GAS REPLACEMENT OF' METAL SULFIDES,

Filed Nov. 15, 1949 4 Sheets-Sheet 4 Ffm-E -t cus #educ/7] Gos minerals.

Patented Dec. 8, 1953 GAS REPLACEMENT oF METAL SULFIDES Edward S. Roberts, New York, and Patrick J. Mc-

Gauley, Glen Cove, N. Y., and Felix Alfred Schaufelberger, Elizabeth, N. J., assignors. to Chemical Construction Corporation, New York, N. Y., a corporation of Delaware Application November 15, 1949, Serial No. 127,452

This invention is concerned with the production of non-ferrous metals broadly, but specically with the production and separation of their sulides. It deals with ores which are mixtures of metal-values minerals and diluents, particularly those which contain copper and at least one other metal value and have iron-bearing minerals and acid-insolubles as diluents and gangue. These ores are treated to convert the metal values content thereof to a solution of soluble salts. From such solutions, the corresponding suldes of the metal values and/or the metals per se are subsequently recovered.

With the increasing utilization, over the past iifty years, of non-ferrous metals, particularly copper, there has steadily grown a demand for improved procedures whereby such metals can be more eiiciently recovered from their ores. Particularly throughout the latter half of this period, repeated attemptsv have been made to devise processes for carrying out this operation chemically.'

Roughly, the overall problem may be broken down into two parts. First, the mineral values must be extracted from the oreby Some successful leaching system.V Second, pure metals must be economically and efficiently recovered from the solutions obtained in the leaching operations. Whether considered as part of the leaching problem, or as part of the metal-recovery problem, there is the additional difficulty, which must be overcome, in that the mixture of metals or their minerals or salts must be separated each from the other.

In the past, largely with respect to the treatment of copper minerals, a number of proposals for such chemical extraction procedures have been presented. Unfortunately, all these operations Suiered from one or more serious defects. As a result, none have been capable of commercial development on a scale commensurate with the possibilities of a Suitable process of this type.

When the wide variety of problems presented by the copper industry alone are considered, this failure is not particularly surprising. For example, it is desirable to4A be able to treat many varieties of copper minerals by the same process, including those of oxidized and sulfide copper When this problem is complicated oy the presence of other minerals, which not only must be rcmovedtherefrom, but also recovered, the complexities of the problem and the previous failures to provide successful solutions thereto become even more readily appreciated. y

Nevertheless, a demand remains in the industry 9 Claims. (Cl. 75-108) 2 for a process capable of easily and economically treating a minerals mixture. It must be adaptable to separate and to recover the copper and other metal values from the gangue and/or diluents. It is, therefore, a principal object of the present invention to provide such a process. It is with the combination of leaching and mineralsseparation that Vthe present invention is concerned. In general, it deals with the treatment of ores which are mixtures of metal-values minerals to obtain one or more enriched concentrates of metal suldes. These may be either mixtures freed from gangue and diluent metals, or individual selected suldes.

Still morespecifically, leach solutions, preferably obtained by acid leaching of the minerals mixture, containing dissolved salts of the metal values, are treated by a replacement reaction. In the latter are employed an additional metal sulfide or metal suldes and a reducing agent. The metal-values suldes are thus precipitated in a mixture of all the sulldes whose solubility is less than that of the added metal sulde. The mother liquor will-contain, as dissolved salts, all the remaining metals-values, i. e., salts o1 those metals the suldes of which are of equal or greater solubility than that of the added sulfide. In addition, it'will contain an amount of dissolved acid salt equivalent to the added metal sulfide reacted in replacing the desired suldes. The desired sulides, as precipitated by the reaction, are collected and treated to reconvert the suldes to solutions of soluble salts. The latter may then be treated further to separate selected sulfides.

Of the previously-proposed processes, perhaps the best is that disclosed in the application for United States Letters Patent, Serial No. 97,224, led June 4, 1949, now Patent No. 2,568,963 issued September 25, 1951. This is by two of the present inventors, P. J McGauley and E. S. Roberts. In that application, copper is separately removed as equivalents of crystallized copper sulfate from liquors obtained by acid leaching of minerals mixtures containing iron and other metal minerals.

In that application, an effective industrial method of separating soluble copper salts from iron and other metal salts, in an acid leach solution containing the copper and other metal suliates, is disclosed. The process involves treatment of the copper-bearing leach solution by replacement with iron suliides, usually that in the ore. When this operation is properly conducted, it results in the complete precipitation of copper from the solution as copper sulfides. It is accompanied by the simultaneous dissolution of an equivalent amount of iron suldes which is converted to ferrous sulfate. The copper suldes are collected by ltratio-n and the filtrate is discarded. The collected copper suldes are oxidized to copper sulfate in solution; and s0 much of the latter as can be crystallized as, pure copper sulfate is separated out and collected. By recirculation, all copper is eventually thus re,- covered.

This device was found to be very useful as a. method of discarding iron andr acid-insoluble diluent metals from a leaching-reduction system Without causing loss of copper` However, when the ore being treated contains other valuable metals, such as cobalt, nickel, zinc, manganese and molybdenum, these metals are also dissolved during leaching but are not recovered. They remain in the leach solution and are removed from the system in the ferrous sulfate liquor. Since these metals arevaluable and are often present in amounts sucient to be proiitably recovered, they cannot be discarded With the fer,- rous sulfatewithout economic loss. The problem of devising a suitable recovery system, which would also recover these additional non-ferrous metals, thus remained unsolved. Preferably, each metal should be recovered as a separate product, if possible.

It is, therefore, a further object of the present invention to devise a separation and recovery system which is capable of recovering these additional non-ferrous metals, as their suldes, with the copper suldes fraction, rather than losing them in the ferrous sulfate solution. In addition, the process should also permit a simple seperation of the resultant suldes mixture into` its separate components,

These objects, as Well as the primary object,` are readily accomplished by the surprisingly effective process of the present invention.Y Broadly, the latter comprises carrying out a replacement reaction on the leach liquor in which the action of one or more replacement metal suldes is supplemented by the action of a reducing agent, preferably a reducing gas.l

In general, the process of the present invention is shown in simplied owsheet form in the accompanying drawings, in which:

Figure l is a representation of a simple flowscheme, showing separation of a mixture of the majority of the Valuable metals in an ore as their sulfides, in a mixture substantially vf ree from all the diluent metals and gangue;

Figure 2 is a modication thereof to obtain the mixture of suliides completely free from suldes of diluent metals;

Figure 3 is the development of a llowscheme for separating the metal suldos mixture obtained by the processes of Figures l and 2 into its components;

Figure l is drawn to a modification of the process of Figure 3 and Figure 5 is a development of a process in which the iowschemes of Figures 3 and 4 are adjusted to handle different requirements.

Several general considerations, applicable to the present invention, should be noted at this point. In the present application, Where the relative solubility of a sulfide is discussed, it is taken as indicated by the solubility product K, i. e., the product obtained by dividing the prod,- uct of the metal ion concentration and the sulfide ion concentration by the concentration of the iin-ionized. sulfide in solution. For purposes Table Solubility Metal sulfide product From the foregoing table, it Will be readily seen that Fes is more soluble than any of the other suliides. listed, with. tlie. exception of that ci Tiiiw fact. is utilised in. tlic, present invention the following While M S. is more. .Soluble than FeS, it is not present in. inout suldc orcs oi non-ferrous metals in appreciable quantities. and economically, the content present therein may usually be discarded in the ferrous Sulfate liquor without approcialclel loss..v Further, man.- eancse sullideI per se neither common nor cheap- It is, therefore not a desirable. suldc for use in the replacement reaction oi the present invention. Iron suliidcs are. botli common and cheap. Therefore, naturally-occurring suldes such as. Fosa, FcS and mixtures thereof make excellent vsuldos to replace other sulfldes from Solution ip. the present processE lf, sulfide. minerals, containing available iron Sulndcs, are added to the. loot pregnant, leach, lio-` uolf containing sulfatos ci suoli, metals as ooppcit nickel, or Whose sulfidcs arc. less soluble than iron goes, into solution as ferrous sulfate. At'the same time, replacement and precipitation oi an equivalent amount o one of the other metals. occurs. metal is .always found to be preferentially that which has tho. next most. insoluble sulfide.

By way of `further illustration, it may be. as,- Sumod that an oie. containing copper and, iron Suliides is to be, lccchcd. with acidf cliic suliatc solution, with oxidation. Such` a case. is Shown in. above-noted McGaulcy and Roberts apr plicatiop. A pregnant. leach liquor,l containing @Opper and iron sulfatos, is obtained.. li this sof lution is then treated with additional amounts of, thc orc, concentrato, Similar reactions to the following would be. expected to. take place:

when is added tc. a not acid solu= tion ci copper sulfate.l HiS is produced according to 1).Y first. .ci this is used up according to (4). Aitor all of the FozQila has been converted to EeSOl, the additional is uocd to precipitate copper according to 22 and 32. These or similar reactions will continuo until all ofl the copper is. precipitated from solution as CuS or Cuzs. Further, if other metal salts, Such as nickel, cobalt, load, or cadmium and the likez the equivalent inctal sulfidcs oi which are more soluble than are also present .in the solution, substantially none of their Sulildcs. Will be precipitated under equilibrium conditions,

unless and until all the copper is replaced and precipitated as its sulfide. In the above-noted McGauley4 and Roberts application, this device is used to separate and purify copper from all the remaining metals. Accordingly, as was noted, these metals are lost from the system in solution with the ferrous sulfate.

Although the present invention is not intended to be limited to a particular theory of operation, it is believed that the incomplete precipitation of suldes other than copper is due to the fact'that oxidation reactions, such as that of Equation 4 above, destroys the (Sn) ions rbefore their concentration becomes great enough to permit the solubilityproduct for one of the other metal suldes to exceed its solubility constant. For example, in the case of nickel sulfide, the sulfide ions are destroyed before the product of their concentration, multiplied by the concentration of the nickel ions, and the product divided by the concentration of the NiS ions in solution, becomes great enough. to exceed the above-noted value, l.4 1024. Above this value of this constant, NiS Will precipitate as a solid. In the process of the present invention, precipitation of all metal suliides less soluble than the replacing sulfides is caused, rather than prevented, as was previously done.

It is also a principal feature of the present invention that an added reducing agent is used, With the added metal sulfide, in the replacement reactions. Thus, an acid salt solution being treated with an added metal sulfide, such as iron suldes, is simultaneously subjected to the action of a reducing agent. It is believed, although once again not intending to limit the invention to any particular theory of operation, that this tends Vto reverse the oxidation reactions, such as thatl of Equation 4 above, and thereby increases the sulfides ion concentration in solution. In this Way, by suitably controlling additions, the replacement reactions may be controlled to completely precipitate suldes of any, or all, of those metals the sulfates of which are in solution, but the suldes of which are less soluble than the replacing metal sulfide, i. e., Fes, i. e., have a lower K value than does the latter.

The application of these principles of the process of the present invention is believed to be well illustrated in Figure 1. As shown therein, an ore concentrate is treated. Such concentrates, ordinarily, form the feed material for the process of the present invention. They may have been obtained by froth flotation, gravity separation, or any other conventional method, wherel,

by a bulk of the gangue constituents is eliminated.

For purposes of illustrative discussion, it may be considered that the representative ore concentrate is one which contains iron, copper, nickel, cobalt, zinc,land manganese only. Other constituents, such as silver, lead, molybdenum and the like, will no doubt be present, at least in small amounts. However, the amounts thereof areeither small enough to be discarded economically or their behavior and treatment will be shown by one of the illustrative metals. This will depend on whether, like manganese, the sulfides are more soluble than FeS or, like copper and zinc, the suli'ldes are less soluble. These facts being true, it simplies the further discussion of the present invention to Vconsider the problem as if these additional metals were not present. After the discussion has been developed, it is believed that ltreatment for any one of these particular suldes,` if desirable, will have Vbeen clearly indicated.

` ore concentrate ofthe above-noted illustrative nature is first sent to some typeof leaching system. The invention is not particularly concerned with the arrangement of .the leaching operation and apparatus. It is quite possible to adapt the overall process to any of the various acid, acid sulfate and ammoniacal leachingV systems or procedures which are now well known.

However, it will be brought out that the replacement reaction of the present process is initiated, and usually is carried out, in an acid solution.` For other than acid leaching, therefore, adjustment of the pH of the leaching solution must be carried out before the replacement reaction is carried out. The latter must be done on a solution of soluble salts, preferably the sulfates. Therefore, while sulfates, or some other equivalent salt, are readily formed in solution after leaching, regardlessof the exact leach liquor used, acid sulfate leaching is usually the most desirable and will be generally taken as .being illustrative inthe following discussion.

Whatever ther leach liquor used, it is added to the ore concentrate in the leaching system. vIn Figure 1, as noted, this is shown as a'n acid leach liquor. Preferably, but not necessarily, air or oxygen or oxygen-enriched air is blown through the mass being leached. The acid sulfate leach liquor, the use of which is illustrated in Figure 1, is also probably preferable, because it is adapted to the treatmentof a greater variety of nonferrous metal ores, including both suldes and oxidized metal minerals.

Specific details of the leaching operation are not an essential feature of the process of the present invention. Leaching is carried out in some known manner, according to conventional practice. Usually, but not necessarily, it is-carried out at elevated temperatures. An acid leaching with concomitant oxidationis highly exothermic. Due to the preferred use of air or oxygen, it is therefore preferably carried out under increased pressure. Conventional apparatus is usually available for the purpose.

The discharge from the leaching system proper comprises a slurry. The latter will contain undissolved solids, principally gangue, and a solution of salts of the minerals values. As shown in Figure 1, this slurry is filtered to remove the residue. The latter is principally gangue and, in the case of Figure 1, an acid-insoluble gangue. If such metals as lead, whose sulfates are insoluble in the leaching solution, are also present in the ore concentrate, these will be removed with this residue. vThis residue, normally, is sent to waste. Various circulating systems, to insure against metal losses in the leaching steps, are conventional.

Although, as noted above, acid leaching is preferred, if a basic leaching system is to be used, the pregnant leach liquor, ordinarily, will be converted to the acid side before the replacement reaction. While a replacement reaction may be carried out in a basic circuit, such a procedure will, ordinarily, involve a considerable amount of additional apparatus, require additional reagents and very appreciably complicate ltration. Accordingly, replacement, as noted above, is preferably carried out in acid solution. Acidication for this or other reasons may be carried out, either before or after filtration. Sincethe illustrative case in Figure 1 is not invelv'ed in basic leaching, this specific modincation is not shown. It is believed that its operation and practice is clearly apparent from the foregoing.

Acidicaticn, if necessary, may be accomplished `by the direct addition of acid. Preferably, however, it should be done by using the basic pregnant leach liquor as part of the leach liquor in carrying out a supplemental oxidation leach, with additional amounts of sulfide ore. In .this Way, neutralizing acid may be formed in situ. This latter process is shown in the copending application for United States Letters Patent, Serial No. 97,226, nled June 4.-, 1949, by Patrick J. McGauley, one of the present inventors, now Patent No. 2,647,827, issued August 4, 1953.

As' shown in Figure l, the metal values are' now present in the filtrate as a solution of soluble sulfatos. This solution is sent to the primary replacement reaction. Here, as noted, it is treated with the metal sulfide and a reducing agent. Replacement may be carried out in any suitable vessel, equipped to carry out chemical reactions under pressure. In the illustrative case, the solution of Cu, Co, Ni, Zn and Mn sulfatos is .treated with added iron sulde. As shown in Figure l, this is preferably from some separate source as fairly concentrated FeS. However, as also shown, if so desired an equivalent amount of the same ore concentrate fed to the leaching system may be used. I n some cases, it may be desirable to use a mixture, partly ore concentrate and partly FeS from some such separate source, such as pyr'itic iron ore.

Whether used `from a separate source of iron sulfides, or as part of the ore concentrate, or as a mixture, there must be available iron and available sulfur present. In the process of Figure 1, the total amount of added iron and sulfur must be at least slightly in excess of the theoretical equivalents required to precipitate suldes of all the replaceable metals whose sulfates are in the pregnant leach liquor.

Ordinarily, .the reaction will be carried out at elevated temperatures. Usually this will be in the range from about 275-750 F. While higher temperatures may be used, there is no particular advantage in so doing. While the lower temperature range places the least restrictions on the apparatus at the lower temperatures, considerably longer periods are required. If an oxidizing acid leach is used, the reaction is exothermi'c. Also, there is no trouble in obtaining the elevated temperature which is preferable in the replacement reaction. The sulfatos solution, coming to the replacement reaction, is already hot. If additional heat is required for further temperature rise, it is readily available from the waste heat that is ordinarily removed by blowing steam from the oxidizing leaching system, to prevent the temperature of the latter from becoming too high.

For the same reason that elevated temperatures are preferred, apparatus equipped for agitation is also desirable. It is not essential to successful operation. However', in general, a replacement which can be carried in one and one-half to two hours at about 450 F. without violent agitation, can be carried out in about one-half hour, at the same temperature, if the pressure vessel is equipped for additional agitation of its contents.

supplementing the action of the added solid suldes is one of the critical features. For this purpose, as noted above, an additional reducing agent, .preferably a gas, is used. Substantially 8 any available reducing gas may be made to serve the purpose. Carbon monoxide, sulfur dioxide and the like, may be used, for example. Hydrogen is, perhaps, even better, as it is an excellent supplement to the hydrogen sulde which is always liberated during the replacement reactions. Mixtures of carbon monoxide and hydrogen are found in various industrial gases, and are usually the most economical and the most readily utilized. Hydrocarbons, Vsuch as methane and ethane, may be used. However, their use alone is not too desirable, because, in some cases, they appear to form complex ions with some of the metals. Their presence, or the presence of sulfurbearing gases, as part of an otherwise desirable and available gas mixture, does not appear to be harmful, in this respect.

The actual consumption of reducing agent is comparatively small. It is necessary only to maintain sufcient concentration to retard or reverse the tendency toward completion of oxidation reactions, such as that discussed above. For this reason, if desirable, or necessary, other and less economical agents may be used. For example, methyl and ethyl alcohol may be used for the purpose. Formic acid, oxalic acid, and the like, formaldehyde in its various commercial forms, and as its sulfoxylates, serve the purpose. Ordinarily, however, the use of a gas will be found more desirable, physically and economically.

Treatment with the added reducing gas, or other agent, and the iron or other metal sulfides is continued until substantially all of the precipitatable suldes less soluble than the treating sulde, i. e., the FeS, have been precipitated. The resultant slurry is filtered, as shown in Figure l. The nitrate is ordinarily removed from the system as an iron discard. The iron, which will be principally present as ferrous sulfate, is, in the illustrative case, the principal diluent metal.

In addition, this solution will contain sulfatos of those metals whose sulfldes are equally, or more, soluble than FeS. In the illustrative case,

these metals are represented by the` manganese.

When they are present in the ore, the filtrate, therefore, will also include such varied metals as magnesium, aluminum, chromium and the like. These are minor constituents and are present in very small amounts. The current practice in treating these ores is to discard these minor fractions. There is no reason why this practice should not be continued in the operation of the present invention, unless an exceptional ore is found. In the latter case, the content of manganese or molybdenum or the like may be suiiiciently high as to warrant special treatment.

The presscake from this filtration will contain any `slight excess of iron sulndes over that required to precipitate the less soluble suldes. In addition, it will contain suliides of all the metals the suldes of which are less soluble than FeS. In the illustrative case, these will be the sulldes of copper, nickel, cobalt and zinc. While this mixture of suldes will contain some iron sulfide, as did the original ore concentrate, the proportions are entirely diierent. The small amount of iron remaining is readily removed.

One additional feature noted in Figure l may be considered. In some cases, the leaching operation may not produce a solution in which the ratio of other metal sulfates to iron sulfate is sulnciently high for a replacement operation of optimum eniciency. If so, a part of the presscake from the filtration may be diverted and 9 y. returned tothe leaching system to supplement the valuable metals content of the ore concentrate being fed thereto. In this way, the solution coming from the leaching operation may be given any desirable ratio of desirable metals to iron. `It is found that from aboutzl .to about 20:1, as ratios in solution, is a good general practice. Y

As Will be seen from the foregoing discussion, replacement by means of the added metal sulfide and the reducing agent can be used to separate the metal values suldes substantially completely from the diluent metals and gangue in the original ore. In some cases, it may be desirable .to insure complete precipitation Without having present these slight excesses of the metal having a sulflde of suicient solubility to be used in the replacement. In the process of Figure. 1, if such complete precipitation is vcarried out, the concentrate will necessarily contain the excess unreacted replacement sulfide. However, instead of. having a metals values to diluent metals ratio of 1:1 or lower, as frequently foundin an original ore concentrate mixture, the product suldes mixture is now substantially Yfree from iron.

When, as noted, it is desirable to have this mixture completely free from` replacement sulfide, this is accomplished by the flowscheme shown in Figure 2.V As shown therein; the result is accomplished by using two replacement reactions. In the iirst, slightly less than the amount of ladded more soluble metal suldes than is stoichiometrically required to replace all the other less soluble sulfides is used. Precipitation will then cease when the ironor other replacementsulde is used up, rather than when the less soluble sulides of the replaced metals are completely precipitated. The so-replaced suldes, free from replacing sulfide, which, in the illustrative case means free from iron, may'then be collected in any desired manner, as by filtration.

As shown in Figure 2, the remaining solution is then subjected to complete precipitation with an excess of added metal sulfide, i. e., iron sulfide. This second, or supplemental, replacement produces a suldes concentratev which is small in amount and contains added metal suldes as Well as replaced metal suldes. This concentrate is collected and is either recycled to the leaching operation, or added with the slurry coming into the primary replacement stage. The latter operation is, perhaps, simpler.

`It might appear that, after stripping the suldeswith a deficiency of soluble metal sulfide, and removal of the desired sulfides concentrate, the residue could be returned directly to the replacement reaction which, Vin Figure 1,:is designated as a primary replacement. ThisV cannot be done, because, except in special circumstances, such a practice would build up anexcess of dissolvedv iron sulfate, or itsequivalent, in the replacement circuit. Y

While the practice of the process ofvFigure 2 is practical, it is, of course, much simpler, and will presumably be preferable, to precipitate'all the mixed suliides by using a: slight excess of iron sulfide, or its equivalent, as in Figure 1. The resultant small amount of iron sulfide contaminant is readily removed later., This was noted above and will be explained more fully below.

A second principal operation of the present inventionoperates in the separation .of theisull0 des mixture concentrate into its component suliides. Commercially, of course, any process which cannot accomplish this result is not particularly useful.` in the past, little helpful information has been availableas to processes suitable for the purpose. 1n general, they were largely conned to tvvo fields, fractional crystallization and selective leaching.

A substantially complete solution `of all the recoverable metal values in an ore is almost a requisite for economical operation. Unfortunately, such a mixture of constituents, ras is found in most sulde flotation concentrates, is completely dissolved only by meansV of acid or acideferric sulfate leaching, generally with oxidation as an Yadded requirement. This Yis the operation preferred in the present invention. Pregnant leach liquorso-obtained can, and often will, contain, for example, iron, copper, cobalt. nickel, manganese, zinc, molybdenum, silver, arsenic, tin, bismuth,l calcium, magnesium, selenium, sodium chloride and other minor items.

Discounting the iron, which in copper recovery is usually a diluent, metalV values of copper. nickel, cobalt, and possibly silver, Zinc, and lead, are the only constituents likely to be present in amounts which Warrant an attempt at their recovery by the present process. As noted above, the remainder is usually present in small amounts only and, in general, may be discarded. If, occasionally, one orV more of these constituents is present in industrially-recoverable amounts, a special circuit can be set up for it. Otherwise, in the practice of the present invention, the custom used in the present industry of discarding these minor constituents is generally followed. v Y Y Reverting to the pregnant leach liquors, the illustrative valuable metal constituents are in solution as soluble salts, generally as sulfates. Unquestionably, the solubilities of these salts is such that little, if any, benefit can be obtained by attempting to separate'them by fractional crystallization. Particularly is this. ti'uein the ratios in which they are usually present in the leach liquors. Industrially, very little has been accomplished in this eld, principally because of the obvious limitations. Y

The other alternative, selective leaching, can be successfully carried out under certain conditions. Using very carefully controlled leaching onhighly suitable ores, thosev ores containing only l.metalsvvhose suldes diier Widely in solubility and in amount, rselective leaching can be employed. Again, unfortunately, such suitable ores are not common. Further, the careful leaching conditions are diicult to establish and to maintain. Even more unsatisfactory, 'complete' leaching ofall the valuable metal substituents is seldom, if ever, possible.

It is, therefore, no small `feature of the presentV invention that it may be readily employed to separate such a suldes mixture as is produced by the processes of Figuresl and 2, intofits components; This is done by'prperly controlledre-v placement. An illustration of its use is shown in Figure 3 of the accompanying drawings'.` The reference to the procedure shown in Figure 3, as noted, indicates the operation being`Y carried out on a mixed slurry. Since, in Figures 1 and 2, a specific mixture was discussed for illustrative purposes, the same mixture Will be discussed throughout the .remainder of this application. The material to be treated, illustratively, according to the process of Figure 3, is the same mixed slurry containing unreacted iron sulfide which is obtained by the preferred operation shown in Figure 1, above.

This slurry is subjected to an acid oxidation. For this purpose, the slurry is combined with a suitable acid, preferably sulfuric acid,.since this sulfate is a desirable salt, and subjected to oxidation by blowing therethrough air, oxygen, or oxygen-enriched air.A The reaction is carried out, preferably, in` the manner 'used in the conventional oxidizing, acid bleaching, discussed above. It is carried ,out under pressure at,4 an elevated temperature of about Z50-750 "Since the Ifelaction is ,exothermid there is no di'iiiculty in ob- ,taining either the pressure or the temperature. Usually, it may be necessary to bleed steam from the operation, in order to prevent excessive ternperature and 'pressure loads upon the apparatus. The lowest practical temperatures and pressures are preferable, as they decrease corrosion 'probleins in the apparatus. The resultant solution of soluble sulfatos is also filtered to remove any insoluble residue. rdinarily, this will only result in the removal of discardable waste material. In some cases, however, the presscake may 'contain a small amount of the material which it is desirable to recover. Usually, this is due to incomplete oxidation in the preceding step. In such cases, this residue is readily passed back to the oxidation f purposes, as `shown in the drawing, this is `con- 'sidere'd to be iron sulfide. In the actuai operation, it will be iron suliide per se, in most cases, because of the large amounts readily available from pyritic iron ores. It may be "ore conce-ntr-ate, if necessary or desirable. An amount stoichiometrically equivalent to the available copper in the i'iitrate is added thereto. Replacement continues until 'precipitation of the copper sulfide is substantially complete.

Solubiiities of various metal suiiides is marke'dlyaffected by the acidity of the solution -in which it is attempted to dissolve them. VI-n the present case, it is desirable to completely precipitate copper sulde, while mainta'iiliing; in solution all the Iother metal 4vsuliides. The resultant iron sul"- fate :should also be retained. `.At a pH above about 2LT-3.0, Yother metal `su-liides, `such as vco'- balt and/'or nickel sulfides, 'tend to precipitate with the copper, and a pH of fabout 2.7 is, therefore, about the maximum desirable limit a-nd 350 is about the limit permissible for suitable operation. On the other extreme, to'o high a concentration -of acid makes it quite difficult to precipitatecopper sulfide. About y15% acid con-tent '1nsolution is approximately the highest acidity which is desirable in this circuit.

fSirice it -is undesirable to precipitate `additional suliides in this particular step; in fact, to the contrary, 'it may be desirable, and it is quite feasible, to add small amounts of air, oxygen, 'or-ferric sulfate to .prevent other metal suliides from lbeing precipitated with the copper; it fis apparent, then, that in vthis one step, the :added 'reducing agent is not necessary. However, added metal sulde `is used in usually substantially -sufci'ent 12 amount to insure, in and of itself, replacement and precipitation of all the copper as copper sulfide. This is collected as product, as shown in Figure 3.

The filtrate, remaining from the removal Aof the copper sulfide, is passed to the second of the suldes separation operations. As shown in the table of the solubility products, above, the next least soluble sulfide, in the illustrative case, is that of cobalt. Accordingly, it is the next to be removed. l Suitable acid conditions for its complete precipitation are in the pI-I rarge of about 3-5. Under favorable conditions, this range may be increased to 2-5 or'2-5.5.

Reduction in the acid content of the solution to the requisite pH may be carried out in any desired manner. Probably the most simple method is the addition of aqueous ammonia, or yan equivalent base, which will not cause precipitation of insoluble metal salts. -I-I-owever, it is usually much more economical to utilize lime, or some similar alkaline-earth metal oxide or hydroxide. In the latter cases, however, the resultant insoluble alkaline-earth metal sulfate must be removed to prevent contamination of subsequently-precipitated metal suliides. To illustrate this procedure, this is the operation shown in Figure 3. At the end of the copper precipitating period, the copper suliide is filtered out, lime is added to the filtrate, and the resultant calcium sulfate precipitate is filtered out. The ycalcium sulfate may be discarded.

Iron suliides, as the illustrative added sulfide, are then added in equivalents to the cobalt sulfate, the equivalent sulfide of which is to be precipitated. Replacement is carried out until precipita-tion substantially ceases. Again, the slurry is filtered'and the cobalt sulde is collected.

In a similar manner, subsequent Areplacement operations are carried out to successfully precipitate sulfides of the remaining dissolved metal salts, i. e., those of nickel and zinc, i-ri the illustrative case. The most favorable pH conditions for replacement of the nickel sulfide is believed to be about 5.0452. vZinc su'lde is most readily precipitated ata -pI-I of from about EQ2 to approximate neutrality. Care lshould be taken not to pass the circuit appreciably to the basic'side at this stage. If such precaution is not taken, it will be ffound that iron suliide is not soluble. The replacement, using iron sulfide therefore, is inoperative.

ABecause definite pif-I Alimi-its to be used in the present process have been specified, does not necessarily `mean that a sulfide replacement for any one metal cannot be carried out lat other pH ranges, particularly when other metals are not present. 'The ranges indicated here `are those which have been Vfound suitable for the separation operations. Also, it should be noted 'that the reaction is being carried out under reducing conditions. Therefore, 'Where the iii-etai suld'e or -siilides being "precipitated are of a metal or metals commonly exhibiting differing valences, all `or a part oi the precipitated sulfides maybe of the met'al o'i lmetais iin 'their 'reduced form.

'The 'iinal iiltrate, which may 'contain some small 'amounts of rmetal values, usually is of insumcient economic value to warrant further treatment. It is, ordinarily, sent to discard, as shown-in Figure 3.

Again, it should be noted that, as discussed above, the illustrative case is limited to certa-iii metals. Others may 'possibly be present in suicient amount 1to fbe vecononiically recoverable. In

i3 that case, 'a separate circuit, therefore, should be set up, utilizing the principles disclosed, with respect to the illustrative metals.

In the above discussion of Figure 3, purity of the precipitated sulfide depended upon using stoichiometric quantities of iron sulfide. As a practical matter, this is somewhat difficult to control. A slight deficiency in the amount of iron sulfide to be used to precipitate a different, particular sulfide, such as that of copper, has two effects. Copper will be precipitated as pure-.copper sulfide; unfortunately, however, not all the copper is precipitated, and this residue is passed into the next stage and becomes a contaminant of the sulfide to be precipitated therein, This is shown in the illustrative case of the cobalt sulfide. Similarly, in each succeeding step, there is danger of carrying over unprecipitated, potentially precipitatable, metal, which will become a contaminant in attempting to recover the next sulfide to be separated.

O'n the other hand, the use of a slight excess of added sulfide over the theoretical equivalents required has an entirely different, but equally undesirable, eiect. The excess metal sulfide, not being reacted, remains as a solid in the slurry, and reports as a contaminant in the same precipitation step. Either result is to be avoided, if possible.

By slight modification of the circuit, this difficulty is readily overcome. Such a modification, as it is to be applied to the illustrative case, is shown in Figure 4. As indicated therein, a mixed sulfates solution, such as that obtained from the oxidation and filtration at the outset of the process of Figure 3, serves as starting material. This solution is then subjected to the first of a plurality of copper sulfide precipitations. In the first, a deficiency oi iron is used. As a result, incomplete precipitation of copper sulfide is obtained. However, the precipitated sulfide so obtained comprises substantially all the copper, and it is substantially pure, i. e., substantially free from other metal suliides. This precipitate is filtered out and recovered as copper sulfide product.

The filtrate, containing the remaining metal values, and the small amount of unprecipitated copper, is then given a second treatment to prec ipitate the copper. In this second treatment, a slight excess of iron sulfide is used. This precipitates all the residual copper sulfide as copper sulfide which is contaminated with the unreacted excess iron sulfide. It does not, however, constitute loss, because, as shown, the solids can be recovered by filtration. The collected mixed suIfides, small in amount, are recirculated as part of the solids fed to the first ycopper sulfide precipitation.

As a result, the second filtrate is then reduced to a pH suitable for the precipitation of the next most insoluble sulfide. As shown in the drawing, aqueous ammonia is used for this purpose, although, as discussed above, as a practical matter, it will usually be cheaper to use lime, burned dolemite, or the like, anda second filter. Ammonia is shown in this drawing in order to simplify the discussion. The pH-increased solution is treated to obtain alfirst cobalt sulde precipitate, using a slight deficiency of replacement sulfide over the Vtheoretical requirements. At the same time, as in the. foregoing discussion, a reducing gas, or equivalent agent, is used. The re- Iii) sultantprecipitate of pure cobalt sulfide is collected by filtration,

sulfides of the metal values having a lower or a higher solubility than the desired sulfide, and from soluble salts. l

While the succeeding steps, in which nickel sulfide and zinc sulfide, in the illustrative case, are not indicated in Figure 4, it is believed that their operation is apparent. These can be carried out inthe same way, modifying the nickel sulfide replacement into two stages, and the zinc sulfide replacement into two stages. The iinal filtrate, after the Zinc sulfide replacement, is again discarded.

K In accordance with the present invention, sulfides other than iron, together with reducing gas,

may be used to replace those metals whose sulfides are less soluble than that of the replacement metal. Illustrative examples may be found in the following representative equations:

Reactions such as those illustrated above may be employed to perform the replacement and separation of separate sulfide products from sulfate solutions, in accor-dance with the present invention. This may be done in one of several ways. The replacement, or replacements, may be carried out on solutions obtained in other processes, or they may be carried out on solutions made expressly for the purpose. Preparation of the latter has been fully illustrated above. It should also be noted that, in the operations discussed above as illustrative, stoichiometric quantities of iron sulfide were reacted with the sulfates solution. Only the metal with the most insoluble metal sulfide is precipitated andl filtered off. The acidic conditions were maintained at the most favorable range for the purpose. The solutions were then treated successively with additional quantities of iron sulfide and additional quantities of reducing agent, thereby successively separate metal sulfides were replaced. This is repeated until the desired separations are accomplished. l

A differing, and in some cases preferable, procedure is shown in the drawings in Figure 5. In the latter procedure, the metal sulfides mixture, instead of being dissolved, as in Figure 3, is divided into two portions. Only one part is oxidized to convert the metal "sulfides into dissolved soluble salts, as was done with the whole sulfides mixture in the process of Figure 3. The remaining portion is filtered and the presscake or residue is discarded, exactly as vwas done in Figure 3. The filtrate, however, receives a distinctly dierent treatment. 4

Rather than ,using iron sulfide to replace the valuable metal constituents, as mixed sulfides, the untreated portion of the sulfides mixture is used to treat the filtrate as the replacing metal sulfide. The filtrate, containing copper, cobalt, nickel, and zinc, is sent to the first copper replacement. Therein, as shown in Figure 5, a

' remaining copper.

'Iiced netal sull'ides portion, 'taken out vas noted above, 'is taken loi s'ulicient 'Weight to have a cobaltplus nickel plus zinc content slightly fdel'cient to the equivalents of available, replaceable copper 'the ltrate. Replacement -is carried out with these mixed sulde's, exactly -as was done with iron sulfide, in Figures v3 and 4. The 'resultant slurry is -iltered vand the presscake f-rom 'the yiilt1-ation step is the substantially pure copper suliide product.

-I'Filtrate is then treated `With enough .more of the divided-up slndes 4to prov-ide a cobalt plus niekel plus Zinc total slightly in excess 'of the In this reaction, the :second copper sulde replacement, the remaining -availaele cep'peris precipitated. As in Figures -3 fand '4, there will be precipitated therewith, the slight excess of mixed sul'des which are unreacted. slur-ry is filtered, land the Vmixed ysuliides arereturned as part of z'the Afeed t'o the first :copper replacement, exactly as was ydone 'in the process of )Figure LIn 'this iway, eventually fall fthe copper reports in the pure copper sulfide .f'ra'ction, lahdall the otheiimetals 'continuefinto the subsequent treatments.

The nitrate, after the removal of copper sulde and -iniXe'dsuli-ides, is fdi-vided finto two portions. -a'chportion is 'treated in a manner analogous'to that used 'in the-copper precipitation. AOne portion is used to-obtain the replacement suldes to be used in thenext step. The remainder is used as the solution, from Which-the next .most insoluble sulde is replaced. (In the illustrative case, therefore-the next step, as was true in Figure 4, is 'the removal difc'obalt.

The iirst portion of thedvided nitrate is sent t'o-afseparatereplacement-operation. Here, it is treated 4with additional 'quantities vof iron sulfide and a reducingiagent, as shown in thedrawing this is-"a gas, :and enough is used to convert the totalco'balt, nickel, andzinc in solution -tofi-nsoluble suldes. Iron sullide, for eXample,-is taken as illustrative, r4because it is usually the Vmost readilyavailable cheap `sulfide for `the purpose.

'Any other available suliide may be used. Itmust,

The Vamountrof sulides mixture used for this' purpose should have a nickel Vplus .zinc content at Aleast equivalent-to the fcobalt insolution. VThe 'solution-is reduced -in `pil-Iacidity to the'approxinia-te value, `as Was (discussed above. SAS was `also notedV above, this may .be vdone most econeunically -by using lime, or other :alkaline-'earth oxide-or hydroxide and an extra lter. Hoyveverftosimplify the nov'vsheet, `the vfextra filter has .been omitted, 'and ammonium" hydroxide has Ib een 'used as the neutralizinga'gent. Itis desirable to use the reducingiagentfat this Stagaraswas noted above, inconnectionfwith the process ofFigure 3 andFigure i4. ETne resultanteslurry sofobtained is filtered. 'Due torthe use offa'slight deciencyzof The resul-tant moval and collection of the latter.

is replacement sul-nde, a 'substantially .pure `cobalt suliide product is obtained. Again, the l'filtrate is treated With a slight excess fof the mixed nickel and zinc sulfides. The resultant precipitation of cobalt suldes, plus .excess suldes, as was the second lcopper precipitate, is recycled to the first cobalt zsulfidereplacement.

'The itr-ate,'which will then be cobalt and copper free, is passed to succeeding ltreatments, as :shown 'iin Fig-ure 5. In each succeeding stage, the saine general .procedure is followed. The ltrate is -divided'i-nto two portions. 'One is treated yWith an 'extraneous sulfide, such as that -of iron, to obtain precipitating sulfides; and the remaining solution is 'treated to obtain the Yproduct sul-nde. -It `is believed that these -successive'treatrnents are apparent from the foregoing discussion. @There should be 'suilicientz-inc available in this Way `to precipitate the nickel. 'This is `indicated `in the Acase `of the 'mixture Abeing taken as illustrative; Since the solution, after removal of the nickel, in the illustrative 'case,vvill contain only zinc, and zinc ycannot Ybe lreadily precipitated with zinc, some additional suliide must .be used for the re- Again We prefer the iron sulfide. However, it is not necessary that 'it be used. "Especially at this stage, the solution is approaching neutrality. 'There jis no reason .why other suldes, such as sodium sulfide, could not be used'to replace Athe zincsulde.

As was noted above-replacement canbecarried out 'in basic solution,..if so desired. I1n .such .a case is sodium suliide, potassiumsulde, Yor :the like, `vvliichcanbeused asthe replacement metal. By .such a procedure, .for example, it -is possible to precipitate manganesesulde from the ferrous sulfate liquor obtained in the-earlierstages of the process. -It is believed-that, iromthe :discussion of ,the .principles of :this case, there :will be .no .difficulty in settingup a circuit vforgthis purpose, if .so desired. Such 'a circuit, for fexample, I.is `highly `convenient if it is necessary to ,recover .a small amount ofegoldromthelsystern. flhegold suliide -is 'most readily :precipitated from basic solution.

'We claim:

.1. Ina'method of 'treating ran ore concentrate, containingl (a) la plurality of non-ferrousf-metal values, (b) acid-insoluble gang-ueand (c) `atleast one `diluent metal, including the `steps of -sub- -jecting the oreconcentrate to 1a leaching 'opera- Stien, '1W-'hereby substantially'all the non-ferrous lmetal values and at 'least part of the diluent .metallare dissolved as vsoluble salts in aqueous in- :organic acid solution, removing theresidual'undissolved solids and-@precipitating from resultant solution# at -least =one` non-ferrous v metal value as an insoluble sulfide thereof; the improvement whichfcomprises: vtreating said-"clarified -solution in -a primary Vreplacement under acid conditions .simultaneously with (fc) at least one replacement :metal sul-fide, the solubility-of ktth-eleast .soluble replacement isuliide, at fthe replacement acidity, .being greater-than that -of the sulfide of atleast' one nonferrousfmetal value to beyprecipitatedcbutnot greater thanthat ofthe sulde of .any diluentimetaL. and (b) reducing agent in sucient..amount` toJinsure11substantiallylno oxidationfoisulde ions" to '-free -sulfur, Wherebyat least/one. 'dissolved nonsferrous metal is precipitated asitlmetalsulde;.fcontinuing treatment unt-il non-ferrous imetalr-rsulde precipitation substantially '..ceases-and collecting 4-resultantfsulfide precipitate.

2. A process according to claim 1 in which said ore concentrate and resultant solution both contain at least one diluent metal and said replacement sulfide is added in slight stoichiometric deflciency to the dissolved non-ferrous metal to be precipitated.

3. A process according to claim 1 in which the reducing agent comprises a gas selected from the group consisting of hydrogen, carbon monoxide and mixtures thereof.

4. In a method of treating an ore concentrate containing (a) a plurality of non-ferrous metal values, including copper, (b) acid-insoluble gangue and (c) at least one iron sulde, including the steps of subjecting the ore concentrate to a leaching operation whereby substantially all the non-ferrous metal values and at least part of iron are dissolved as soluble sulfates in aqueous sulfuric acid solution, removing the residual undissolved solids and precipitating from resultant solution at least one non-ferrous metal value as an insoluble sulde thereof; the improvement Which'comprises: treating resultant clarified solution in a primary replacement under acid conditions simultaneously withV (a) an iron suliide and (b)l a reducing agent in sulicient amount to insure substantially no oxidation of sulde ions to free sulfur; continuing the treatment until non-ferrous metal sulfide precipitation substantially ceases and collecting resultant sulde precipitate.

5. A process according to claim 4 in which said non-ferrous metal sulfide precipitation is carried outat a pH less than about 3 but an acid content of less than about 15% by Weight.

6. A process according to claim 4 in which iron sulfide as the replacement sulfide is utilized in slight excess over the stoichiometric equivalents required to precipitate all the non-ferrous metal sulfldes less soluble than FeS.

7. A process according to claim 4 in which the replacement iron sulde is added in slight stoichiometric deficiency to the amount required to replace all the non-ferrous metal suldes less soluble than FeS; treatment is continued until all the added iron sulfide is in solution; resultant iron-free precipitated solid suldes are collected; residual solution is treated with a stoichiometric excess of added iron sulfide; treatment is continued until precipitation substantially ceases, whereby a second sulfides precipitate is obtained, and said second suldes concentrate is collected.

8. A process according to claim 7 in which said second suldes concentrate is recycled as feed to said primary replacement.

9. In a method of treating an ore concentrate, containing (a.) a plurality oi non-ferrous metal values, (b) acid-insoluble gangue and (c) at least one diluent metal, including the steps of subjecting the ore concentrate to a leaching operation -Whereby substantially all the non-ferrous metal values and at least part of the diluent metal, are dissolved as soluble sulfates in aqueous sulfuric acid solution, removing the residual undissolved ksolids and precipitating from resultant solution at least one non-ferrous metal value as an insoluble sulde thereof; the improvement which comprises: treating said claried solution in a primary replacement under acid conditions simultaneously with (a) about a stoichiometric equivalent to dissolved non-ferrous metal values of at least one replacement metal sulde, the solubility of all replacement sulfides, at the replacement acidity, being greater than that of the suldes of all non-ferrous metal values to be precipitated but not greater than that of any diluent metal, and (b) a reducing agent in sumcient amount to insure substantially no oxidation of sulde ions to free sulfur, whereby substantially all dissolved non-ferrous metals are precipitated as mixed metal suliides; continuing treatment until non-ferrous metal sulfide precipitation substantially ceases; collectingresultant mixed suldes precipitate; and subjecting collected mixed suldes to oxidation in the presence of free inorganic acid, whereby said suldes are converted to a substantially diluent metal free solution of mixed dissolved non-ferrous metal salts.

EDWARD S. ROBERTS. PATRICK J. MCGAULEY.

FELIX ALFRED SCHAUFELBERGER.

`References Cited( in the le of this patent UNITED STATES PATENTS Number .Name Date f 1,333,688 Sulman et al Mar. 16, 1920 k1,857,494 Carson May 10, 1932 1,890,934 Carson Dec. 13, 1932 1,983,274Y Earle Dec. 4, 1934 2,094,277 Mitchell Sept. 28, 1937 2,296,423 Clark Sept. 22, 1942 2,326,592 Wicker Aug. 10, 1943 OTHER REFERENCES Mellor, J. W. Comprehensive Treatise on Inorganic and Theoretical Chemistry, Longmans. Green & Co. (1935), New York, N. Y., vol. 14, page 143. 

1. IN A METHOD OF TREATING AN ORE CONCENTRATE, CONTANING (A) A PLURALITY OF NON-FERRROUS METAL VALUES, (B) ACID-INSOLUBLE GANGUE AND (C) AT LEAST ONE DILUENT METAL, INCLUDING THE STEPS OF SUBJECTING THE ORE CONCENTRATE TO A LEACHING OPERATION, WHEREBY SUBSTANTIALLY ALL THE NON-FERROUS METAL VALUES AND AT LEAST PART OF THE DILUENT METAL ARE DISSOLVED AS SOLUBLE SALTS IN AQUEOUS INORGANIC ACID SOLUTION, REMOVING THE RESIDUAL UNDISSOLVED SOLIDS AND PRECIPITATING FROM RESULTANT SOLUTION AT LEAST ONE NON-FERROUS METAL VALUE AS AN INSOLUBLE SULFIDE THEREOF; THE IMPROVEMENT WHICH COMPRISES; TREATING SAID CLARIFIED SOLUTION IN A PRIMARY REPLACEMENT UNDER ACID CONDITIONS SIMULTANEOUSLY WITH (A) AT LEAST ONE REPLACEMENT METAL SULFIDE, THE SOLUBILITY OF THE LEAST SOLUBLE REPLACEMENT SULFIDE, AT THE REPLACEMENT ACIDITY, BEING GREATER THAN THAT OF THE SULFIDE OF AT LEAST ONE NON-FERROUS METAL VALUE TO BE PRECIPITATED BUT NOT GREATER THAN THAT OF THE SULFIDE OF ANY DILUENT METAL, AND (B) REDUCING AGENT IN SUFFICIENT AMOUNT TO INSURE SUBSTANTIALLY NO OXIDATION OF SULFIDE IONS TO FREE SULFUR, WHEREBY AT LEAST ONE DISSOLVED NON-FERROUS METAL IS PRECIPITATED AS METAL SULFIDE; CONTINUING TREATMENT UNTIL NON-FERROUS METAL SULFIDE PRECIPITATION SUBSTANTIALLY CEASES AND COLLECTING RESULTANT SULFIDE PRECIPITATE. 